It's not required to use ES6 to perform the operation you're asking about. You could use either of the following:
/**
* The last value in the array, `3`, is at the '2' index in the array.
* To retrieve this value, get the length of the array, '3', and
* subtract 1.
*/
const items = [1, 2, 3];
const lastItemInArray = items[items.length - 1] // => 3
or:
/**
* Make a copy of the array by calling `slice` (to ensure we don't mutate
* the original array) and call `pop` on the new array to return the last
* value from the new array.
*/
const items = [1, 2, 3];
const lastItemInArray = items.slice().pop(); // => 3
However, if you are dead set on using ES6 to retrieve this value we can leverage the spread operator (which is an ES6 feature) to retrieve the value:
/**
* Create new array with all values in `items` array. Call `pop` on this
* new array to return the last value from the new array.
*
* NOTE: if you're using ES6 it might be a good idea to run the code
* through Babel or some other JavaScript transpiler if you need to
* support older browsers (IE does not support the spread operator).
*/
const items = [1, 2, 3];
const lastItemInArray = [...items].pop(); // => 3